Understanding the Connection Between Vitamin D and MS
Multiple sclerosis (MS) is one of medical science's biggest
mysteries. It's entirely unclear what causes this chronic autoimmune disease.
For years, many researchers have been pointing out a possible connection
between the prevalence of multiple sclerosis and sunlight
exposure—specifically, in terms of the role ultraviolet radiation in our
bodies' vitamin D production. And, while the link between vitamin D and MS
remains fuzzy at best, new findings have further spiked interest in the
Recent studies show what appears to be a negative correlation
between exposure to UV radiation and MS. In other words, the lower the exposure
to radiation from the sun, the higher the risk of MS.
Due to the Earth's shape and its rotation around the sun, the
intensity with which sun radiation hits different regions of the planet will
depend on their latitudes—the closer to the equator, the higher the intensity.
The underlying idea is that less radiation hinges the body's natural production
of vitamin D and, thus, could lead to a higher risk of developing MS.
The purpose of this tool is to allow us to visualize this
possible relation between sun radiation—measured by the ultraviolet index—,
vitamin D rates, and MS prevalence throughout the world.
So, is there a connection?
What Our Data Tool Found
By comparing countries with similar standards-of-living, but
at different latitudes, you can quickly begin to see how sun exposure and
vitamin D rates might affect how common MS is.
For example, Canada has one of the world's highest rates of MS
and, due to the country's distance from the equator, its residents get
considerably lower levels of UV radiation.
In comparison, the United States has an average UV index twice
as high as its neighbor's and MS rates almost half as low.
Even within the same country, MS prevalence rates seem to
increase in areas further from the equator. A recent study published in the Journal of Allergy and Clinical Immunology
showed that North of Scotland has the highest rates of MS in the United Kingdom
(Milliken, et al., 2012).
Similarly, another study by the University of Tasmania in Australia, concluded
that Tasmanians were "seven times more likely to have MS than people in
Northern Queensland and the Northern Territory" (Stewart, et al., 2012).
The same case could be made for neighboring countries such as
France and Germany where, while sharing a similar geography, their small
difference in latitude—Germany is about five degrees farther north—makes for a
big difference in terms of the variables we're looking into:
Unfortunately, the relationship between sun radiation exposure
and vitamin D rates doesn't always come across so clear.
For example, take the country Spain. Spain sits at similar
latitude to the U.S., and, as a result experiences similar UV indexes.
Nonetheless, the U.S.'s vitamin D rate almost doubles that of Spain.
Why is that? It's hard to say. While sunlight is the main
source of vitamin D, eating habits and the use of of vitamin D supplements can
also play a role. While no major studies have been done comparing the average
Spanish diet to an American diet, it may be the case that Americans tend to get
more dietary vitamin D. For example, pay attention to your orange juice
tomorrow at breakfast—you may not have noticed before, but many brands of
orange juice "infuse" their product with vitamin D.
The Bottom Line
What is fairly clear is that MS is more prevalent in certain
geographical areas, and these all tend to be further from the equator. High latitudes
and, therefore less exposure to intense sunlight means a higher risk for MS.
What is less clear is why.
The connection between vitamin D, sun exposure, and MS remains
unclear. The good news is that some of our best scientists are on it. For
example, Australian researchers are about
to launch the world's first large-scale clinical trial to measure vitamin
D's effectiveness as a preventative treatment for MS.
In the meanwhile, here are some additional resources to learn
more about MS: